1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a main pole that produces a magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For higher recording densities, it is necessary to prevent adjacent track erasure.
A known technique for preventing adjacent track erasure induced by a skew is to configure the main pole so that its end face located in the medium facing surface decreases in width with increasing proximity to the top surface of the substrate, as disclosed in U.S. Patent Application Publication Nos. US 2004/0150910 A1 and US 2009/0059426 A1, for example. U.S. Patent Application Publication Nos. US 2004/0150910 A1 and US 2009/0059426 A1 also disclose configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface.
In order to prevent skew-induced problems, it is also effective to reduce the thickness of the main pole in the medium facing surface. If the entire main pole is thinned, however, the main pole becomes small in cross-sectional area perpendicular to the direction in which magnetic flux flows. This makes it difficult for the main pole to direct much magnetic flux to the medium facing surface, thus leading to degradation of overwrite property.
Configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface as disclosed in U.S. Patent Application Publication Nos. US 2004/0150910 A1 and US 2009/0059426 A1 allows the main pole to be small in thickness in the medium facing surface and allows part of the main pole away from the medium facing surface to be large in thickness, thereby making it possible for the main pole to direct much magnetic flux to the medium facing surface.
In order to prevent adjacent track erasure induced by a skew and provide higher recording densities, it is effective to provide a write shield having an end face that is located in the medium facing surface at a position on the front side in the direction of travel of the recording medium relative to the end face of the main pole, as disclosed in U.S. Patent Application Publication No. US 2009/0059426 A1.
A magnetic head having the write shield is typically provided with a return path section for connecting the write shield to part of the main pole away from the medium facing surface. The write shield, the return path section, and the main pole define a space through which part of a coil passes. The write shield and the return path section have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. The write shield and the return path section also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole.
The position of an end of a record bit to be recorded on the recording medium depends on the position of an end of the end face of the main pole located in the medium facing surface, the end being located on the front side in the direction of travel of the recording medium. In order to define the position of the end of the record bit accurately, it is therefore important that the write shield have an end face that is located in the medium facing surface at a position on the front side in the direction of travel of the recording medium relative to the end face of the main pole and that this end face of the write shield capture a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium. The magnetic head having the write shield is capable of preventing adjacent track erasure and provides a further improved recording density.
In view of the foregoing, in order to prevent adjacent track erasure induced by a skew and provide a higher recording density, the magnetic head can conceivably be configured so that part of the top surface of the main pole in the vicinity of the medium facing surface is formed into an inclined portion that is inclined relative to a direction perpendicular to the medium facing surface, and the write shield is provided with an inclined surface opposed to the inclined portion of the main pole, as disclosed in U.S. Patent Application Publication No. US 2009/0059426 A1.
The above-described configuration, however, has a problem in that where the inclined portion of the top surface of the main pole and the inclined surface of the write shield are opposed to each other over a large area with a small spacing therebetween, magnetic flux leakage from the main pole to the write shield increases to cause degradation of write characteristics such as the overwrite property.
To avoid this, as disclosed in U.S. Patent Application Publication No. US 2009/0059426 A1, the inclined portion may be made smaller than the inclined surface in length in the direction perpendicular to the medium facing surface. In this configuration, the inclined surface includes a first portion opposed to the inclined portion, and a second portion that is contiguous with the first portion and is located farther from the medium facing surface than is the first portion. The distance between the second portion and part of the top surface of the main pole that is located farther from the medium facing surface than is the inclined portion is greater than the distance between the first portion and the inclined portion of the top surface of the main pole. This makes it possible to prevent magnetic flux leakage from the main pole to the write shield.
As the frequency of a write signal is increased to achieve a higher recording density, the magnetic head is required to provide an improved rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement, it is effective to reduce the length of a magnetic path that passes through the write shield, the return path section and the main pole. However, the following problem will occur with the aforementioned configuration in which the inclined portion is smaller than the inclined surface in length in the direction perpendicular to the medium facing surface. In this configuration, due to the large distance between the second portion of the inclined surface and the part of the top surface of the main pole that is located farther from the medium facing surface than is the inclined portion, the space defined by the write shield, the return path section and the main pole, through which part of the coil passes, is also large. Thus, it is not possible to sufficiently reduce the length of the magnetic path that passes through the write shield, the return path section and the main pole.